1. Field of the Invention
The present invention relates to a polyamide resin composition and a molded article obtained therefrom and excellent in surface gloss. More particularly, it relates to a polyamide resin composition and a molded article obtained therefrom which are excellent in the surface gloss required for interior and exterior automotive trims, official appliance parts and sports and leisure goods and high in strength and rigidity and dimensional stability in the actual use and furthermore, excellent in characteristics such as thermal aging resistance, light resistance, discoloration resistance and light transmission.
2. Related Art
Recently, polyamide resins are increasingly utilized as interior or exterior structural members taking advantages of their excellent mechanical properties, high reinforcing effect obtained by reinforcing them with inorganic fillers such as glass fibers and excellent colorability and processability.
The high surface gloss, strength and rigidity and dimensional stability are performances required in common for structural members. Among them, the surface gloss is greatly influenced not only by the design of mold including the gate position, size and shape and molding conditions, but also by the flowability of resins in the mold and solidification conditions. Especially, compositions containing inorganic fillers such as glass fibers are apt to undergo deterioration of surface gloss due to the partial rising of the inorganic fillers to the surface of molded articles. Such molded articles having a low gloss are inferior in appearance, resulting in not only reduction of commercial value, but also deterioration of slidability with other materials.
For satisfying the high strength and rigidity and dimensional stability, it is generally known to incorporate inorganic fillers such as glass fibers into resins. However, it is known that when amount of the inorganic filler is increased in an attempt to increase the strength and rigidity and dimensional stability, the surface gloss of the molded articles deteriorates. Accordingly, in order to obtain molded articles excellent in gloss and besides high in strength and rigidity and dimensional stability, hitherto, the amount of the inorganic filler is reduced to such an extent that the filler does not rise to the surface and the reduction of strength and rigidity and dimensional stability caused by the reduction of the amount is compensated by contriving the shape of the articles, such as increase in wall thickness or strengthening with ribs.
On the other hand, resin materials which are not damaged in their surface gloss while increasing the amount of the inorganic fillers as much as possible have also been developed. They are proposed, for example, in Japanese Patent Kokoku No. 61-60861 and Japanese Patent Kokai Nos. 63-118367, 2-265965, 3-269056, 4-77554 and 4-149234.
Among them, as disclosed in Japanese Patent Kokai No. 2-265965, owing to absorption of water, the strength and rigidity of polyamide resins comprising the combination of only aliphatic polyamides such as nylon 6, nylon 66 and nylon 66/6 copolymers are greatly influenced by the temperature and humidity of the atmosphere where they are actually used and so these polyamide resins are restricted in their use.
Furthermore, as disclosed in Japanese Patent Kokoku No. 61-60861 and Japanese Patent Kokai Nos. 63-118367, 3-269056 and 4-149234, reduction in strength and rigidity due to absorption of water and in dimensional stability can be improved to some extent by using polyamide resins having monomer components containing an aromatic ring such as terephthalic acid and isophthalic acid. However, according to these techniques it has been difficult to obtain molded articles having satisfactorily high surface gloss because the resin compositions containing inorganic fillers are inferior in flowability or the solidification rate of the resins in the mold is high. In order to obtain molded articles of high surface gloss using these resins, there is a method of raising the mold temperature as high as possible, but there occurs a new problem that the molding time cycle is prolonged. Furthermore, as the larger mold is used, it becomes difficult to uniformly raise the temperature of the whole inside of the mold. Besides, in the case of the mold of complicated design having ribbed structure, locally high temperature area or locally low temperature area is formed and the resulting molded article have portions of high surface gloss and low surface gloss as a whole. Accordingly, for obtaining molded articles having high surface gloss over the whole surface, a resin composition capable of developing a high gloss in a wide mold temperature area is needed and none of the conventional materials have satisfied this requirement.